I can be anyone you want me to be.
The Siren is a minor character on Once Upon a Time. She was the guardian of Lake Nostos, an enchanted lake with mystical and magical powers, including powers of healing and regenerating. The siren was a malevolent creature that lured men into her waters and killed them. She posed as Snow White to attract Prince Charming, but he was able to resist her thrall and killed her.
Before the Curse
The Siren is killed by Charming. ("What Happened to Frederick")
Princess Abigail recruits Prince Charming to help her save her true love, Frederick, from a curse that left him trapped in a solid gold form after being touched by her father, King Midas. She asks him to go on a dangerous quest to a place called Lake Nostos, which is guarded by a siren, as the waters from the lake would be able to help Frederick. When Charming arrives at the lake and collects the water, he is met by the siren. When she emerges from the water, Charming is stunned by her beauty. She tries to seduce him, but he stays strong and resists her. However, she takes on the form of his true love, Snow White, and tries to seduce him again. Despite knowing it is an illusion, Charming falls for her tricks and begins to kiss her in the middle of the lake. The siren then suddenly turns on Charming and drags him under the water to kill him. However, after a struggle, Charming manages to stab the siren, killing her, and returning her to her normal form. ("What Happened to Frederick")
Charming finds the Siren's remains. ("Lady of the Lake")
A long while later, when Prince Charming's mother, Ruth is shot by an arrow fired by King George's men, he, Snow White and Lancelot decide to take her to Lake Nostos so they can use it's waters to heal Ruth's injuries. On the way, Charming and Lancelot scout ahead to find the lake, leaving Snow and Ruth to talk. Snow reveals that she was cursed by King George so she cannot bear a child. Ruth assures the young woman that if the waters can heal her injuries, then they can break her curse. When they arrive at the lake, they are horrified to discover that it has all dried up. They look around for any possible remaining water, but all Charming can find is the remains of the Siren and her tiara; this causes him to believe that once the Siren died, the lake dried up. Lancelot tells them to fear not as he was raised by a lake, promising there may be some water remaining. He finds a sip-worth of water in a small shell and this is used on Snow White, this allowing her to conceive. However, this was only possible because Ruth sacrificed her life for Snow and Charming's future child as she refused to drink the water. ("Lady of the Lake")
Gallery of photographic stills released to promote the character.